The present invention relates to a watertight brushless fan motor and a manufacturing method thereof.
Generally, brushless fan motors include a stator provided with a plurality of stator magnetic poles, a circuit substrate fixed to the stator, a rotor for rotating with respect to the stator, and a case. The case includes a bearing supporting cylindrical section in which a bearing for rotatably supporting the rotary shaft of the rotor is received, a cylindrical housing section for surrounding the outer periphery of the rotor, a plate-like section separated from the circuit substrate with a predetermined space and extending from the end of the bearing supporting cylindrical section in a direction perpendicular to the center line of the bearing supporting cylindrical section, and a plurality of webs for connecting the plate-like section to the housing section. In the brushless fan motor of this type, it is required that the stator and the circuit substrate be made watertight. Then, as disclosed in Japanese Patent Application Laid-Open Publication No. 191611/1998, a watertight brushless fan motor has been proposed in which spaces between the plate-like section and the bearing supporting cylindrical section of the case are formed with an insulating resin in such a manner that the stator and the circuit substrate are included inside, thereby forming a molded part.
However, in this conventional watertight brushless fan motor, when the insulating resin is molded, the insulating resin shrinks due to what is called a molding shrinkage or molding sink, or expands or shrinks due to a change in ambient temperature, thereby causing a crack in the outer surface of the molded part.
It is therefore an object of the present invention is to provide a watertight brushless fan motor which can prevent occurrence of a crack in the outer surface of a molded part caused by shrinkage of an insulating resin resulting from the molding shrinkage, or expansion and shrinkage of the insulating resin due to a change in ambient temperature, and a manufacturing method of the watertight brushless fan motor.
It is another object of the present invention to provide a watertight brushless fan motor in which an insulating resin can be molded, with the center line of the cylindrical body of the die of a resin mold aligned over the center line of the bearing supporting cylindrical section of the case, and a manufacturing method of the watertight brushless fan motor.
A watertight brushless fan motor, the improvement of which is aimed at in the present invention, includes: a stator provided with a plurality of stator magnetic poles, each of which has a winding wound around each of a plurality of projecting pole portions of an iron core constituted by a plurality of laminated steel plates; a circuit substrate mounted with electronic components constituting a control circuit for controlling a current flow through the winding, fixed to the stator, and spaced from the projecting pole portions at a predetermined distance; a rotor including a plurality of rotor magnetic poles, each of which is made of a permanent magnet, on an inner peripheral side thereof and including a plurality of blades on an outer peripheral side thereof; a case; one or more pads; and a molded part. The case includes a bearing supporting cylindrical section in which a bearing for rotatably supporting the rotary shaft of the rotor is received, a cylindrical housing section for surrounding the outer periphery of the blades of the rotor, a plate-like section extending from the end of the bearing supporting cylindrical section in a direction perpendicular to the center line of the bearing supporting cylindrical section with a predetermined space formed between the plate-like section and the circuit substrate, and a plurality of webs for connecting the plate-like section to the housing section. One or more pads are disposed in at least one of a first space between the stator and the circuit substrate and a second space between the circuit substrate and the plate-like section of the case, and made of an electrical insulating material. The one or more pads occupy the main portion of one of these spaces or both. The molded part is formed with an insulating resin in such a manner that the stator, the circuit substrate, and the one or more pads are included therein. Incidentally, at least one of the first and second spaces has such a capacity that a molding shrinkage occurs in the surface of the molded part when the molded part is filled with the insulating resin alone.
Generally, when the insulating resin is molded, the insulating resin in the molded part with an increased thickness is pulled toward the center of the molded part at the time of curing. Consequently, a phenomenon in which the outer surface of the molded part is transformed, or a molding shrinkage occurs. At a boundary between portions of the molded part of different thickness, when the insulating resin has expanded or shrunk due to a change in ambient temperature, a crack occurs in the outer surface of the molded part. Then, according to the present invention, if a pad is disposed in at least one of the first space between the stator and the circuit substrate and the second space between the circuit substrate and the plate-like section of the case, the thickness of the molded part can be reduced. With this arrangement, the molding shrinkage of the insulating resin at the time of curing can be reduced. Further, the pad can reduce an unbalance in the thickness of the insulating resin of the molded part. For this reason, the amount of expansion and shrinkage of the insulating resin due to a change in ambient temperature can be reduced, thereby allowing prevention of occurrence of a crack in the outer surface of the molded part.
Since the first space formed between the stator and the circuit substrate, in particular, is adjacent to the rotor, the molded part is formed according to the shape of the rotor. Thus, formation of portions of the molded part of different thickness is apt to occur. For this reason, it is desirable to dispose one or more pads that prevent occurrence of a crack in the outer surface of the molded part due to expansion and shrinkage of the insulating resin.
Generally, in the watertight brushless fan motor, the improvement of which is aimed at according to the present invention, the molded part includes a first molded part having the stator and a second molded part having such a shape and dimension as to include the circuit substrate and form a step portion for the first molded part. In this case, since the step portion is formed at a boundary between the first molded part and the second molded part, a crack is apt to occur notably at this boundary. Consequently, it is preferable that the shapes and the dimensions of one or more pads disposed in the first space are defined so as to suppress occurrence of a crack at the boundary between the first molded part and the second molded part due to expansion and shrinkage of the insulating resin. Specifically, one or more pads disposed in the first space are constituted by a single first pad. The first pad includes a cylindrical section fitted into the bearing supporting cylindrical section and a plate-like section extending radially outward from the cylindrical section. The plate-like section is formed with a plurality of slits into which part of the windings of the stator magnetic poles are inserted. With this arrangement, only by inserting the cylindrical section into the bearing supporting cylindrical section of the case, the first pad can be disposed generally across the entire first space. Thus, just a simple-shaped pad can enhance the effect of preventing the molding shrinkage. At the end of the plate-like section located radially outward, curved surface extended sections are integrally formed extending both in a circumferential direction of the bearing supporting cylindrical section and in a center line direction of the bearing supporting cylindrical section and have curved surfaces respectively curved along magnetic pole faces of the projecting pole portions. With this arrangement, the insulating resin is thinly molded on the curved surface extended sections, thereby allowing effective prevention of occurrence of a crack at the boundary between the first molded part and the second molded part. In this case, the length of the curved surface extended sections in the center line direction may be the length corresponding to a portion of the first molded part facing the rotor, positioned on the side of the circuit substrate rather than on the side of the iron core.
One or more pads disposed in the second space can be constituted by a single second pad. In this case, the second pad may include a cylindrical section fitted into the bearing supporting cylindrical section and a plate-like section extending radially outward. With this arrangement, only by fitting the cylindrical section into the bearing supporting cylindrical section of the case, the second pad can be disposed generally across the entire second space. Thus, just a simple-shaped pad can enhance the effect of preventing the molding shrinkage. When a part of the electronic components are mounted at the back of the circuit substrate facing the plate-like section of the case, at least one through hole for letting an electronic component large in size and dimension pass therethrough may be formed in the plate-like section of the second pad so as to facilitate positioning of the second pad.
Various materials can be employed for the insulating resin. However, if an urethane resin is employed, a curing time can be reduced, and a watertight effect can be obtained at low cost.
In a manufacturing method of a watertight brushless fan motor, first, a stator assembly combining a stator and a circuit substrate, a case, a die, and an annular member are prepared. The case includes a bearing supporting cylindrical section, a plate-like section extending from the end of the bearing supporting cylindrical section in a direction perpendicular to the center line of the bearing supporting cylindrical section and an outside cylindrical section extending from the outer end of the plate-like section in a direction of the center line of the bearing supporting cylindrical section along the bearing supporting cylindrical section. The die includes a cylindrical body and a blockage wall having an engaging portion that can be engaged with the bearing supporting cylindrical section, for blocking one opening of the cylindrical body. The other opening of the cylindrical body is blocked by the plate-like section and the outside cylindrical section of the case with the die being fixed to the case. The annular member is made of a resin and is mounted or fitted to the die. When the die is fixed to the case, the annular member aligns the center line of the cylindrical body of the die over the center line of the bearing supporting cylindrical section with the inner peripheral end surface of the annular member being brought into contact with the outer peripheral surface of the outside cylindrical section. Then, the stator assembly is mounted on the bearing supporting cylindrical section of the case. Next, the bearing supporting cylindrical section is engaged with the engaging portion, the inner peripheral end surface of the annular member is brought into close contact with the outer peripheral surface of the outer cylindrical section of the case, and then the die mounted with the annular member is attached to the case. Next, the die and the annular member are fixed to the case. Then, an insulating resin is poured into the die to mold spaces between the plate-like section and the bearing supporting cylindrical section with the insulating resin in such a manner that the stator and the circuit substrate are included inside. According to the method of the present invention for molding with a resin, the annular member made of a resin can shield the die and the outside cylindrical section of the case. In addition, the insulating resin can be molded by aligning the center line of the cylindrical body of the die over the center line of the bearing supporting cylindrical section. For this reason, it is possible to prevent contact of the insulating resin into the rotor due to misalignment between the center line of the cylindrical body of the die and the center line of the bearing supporting cylindrical section.
In this case, in order to perform molding, in at least one of the first space between the stator and the circuit substrate and the second space between the circuit substrate and the plate-like section of the case, one or more pads made of an electrical insulating material for occupying the main portion of one of these spaces or both should be disposed.
Further, it is preferable to perform molding by pouring the resin under low vacuum. With this arrangement, molding can be performed with no air bubbles remaining therein.
According to the present invention, a pad is disposed in at least one of the first space between the stator and the circuit substrate and the second space between the circuit substrate and the plate-like section of the case. Thus, the thickness of the molded part can be reduced. For this reason, a molding shrinkage at the time of curing of the insulating resin can be reduced. Further, an unbalance of the thickness of portions of the molded part made of the insulating resin can be reduced. Hence, the amount of expansion and shrinkage of the insulating resin due to a change in ambient temperature can be reduced, thereby allowing prevention of occurrence of a crack in the outer surface of the molded part